The present invention relates to a motor drive device and an electronic timepiece.
In stepping motors, the rotor must be reliably rotated to each step. Therefore, a drive controller for a stepping motor applies a drive pulse to rotate the rotor and then detects the counter-electromotive force (reverse voltage) generated due to damping when the rotor stops at a prescribed step angle in order to determine whether the rotor rotated (rotor rotation detection). If it is determined that the rotor did not rotate, an additional correction pulse is applied to rotate the rotor.
Rotation detection technology for single-coil clock motors has already been developed. For example, Japanese Patent Application Laid-Open Publication No. H9-266697 discloses the following: “Drive pulses supplied to a step motor are controlled using a chopper scheme in which the duty cycles of initial and final drive pulses are set lower than the duty cycle of interim drive pulses. This makes it possible to achieve a low effective power distribution in the initial and final drive pulses and a high effective power distribution in the interim drive pulses, thereby making it possible for the step motor to generate a torque equal to its own cogging torque.
This, in turn, reduces unnecessary power consumption during the initial and final drive pulses and makes it possible to rotate the rotor at low speeds, thereby making it possible to reduce overall power consumption when driving the step motor.”
Another well-known conventional technology is dual-core stepping motors, which include two coils and can be rotated in either direction by applying drive pulses to the coils as appropriate. Rotation detection technology has not yet been developed for this type of dual-core motor. One possible rotation detection method would be to increase the impedance of one of the two coils in the dual-core motor to a high value during detection in order to increase the magnitude of the electromotive force needed to detect rotation, for example. However, with this type of simple approach, the electromotive force could potentially become large enough to be misdetected as rotation even when the rotor is not actually rotating, such as due to environmental factors including sample variation or high temperatures.